The inventive concept relates generally to electronic memory technologies. More particularly, the inventive concept relates to a variable resistance memory devices and related methods of operation.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Examples of volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM). Examples of nonvolatile memory devices include ferroelectric random access memory (FRAM), magnetic RAM (MRAM), phase change memory device, resistive RAM (RRAM), and flash memory.
There has been an increasing demand for nonvolatile memory devices in recent years due to a variety of technology trends, such as the proliferation of mobile devices requiring persistent data storage, as well as a general increase in the demand for personal data storage. Accordingly, researchers continue to invest resources in improving existing nonvolatile memory technologies and developing new ones.
RRAM is one type of nonvolatile memory that has showed promise. In particular, RRAM has demonstrated potential for high speed, high capacity, and low power consumption. A variable resistance material film of the RRAM shows a reversible resistance variation according to a polarity or a magnitude of an applied pulse. In some types of RRAM, a colossal magnetro-resistive material layer (CMR) has a perovskite structure or a metal oxide layer with a conductive filament that is generated or disappears in response to an electric pulse and is used as a variable resistance material film. A memory including such a variable resistance material film can be referred to as a variable resistance memory.
In general, a variable resistance memory element can be classified as a unipolar element or a bipolar element according to a polarity of a write pulse. In the case of a unipolar variable resistance element, a polarity of a set pulse is identical to that of a reset pulse. In the case of a bipolar variable resistance element, a polarity of a set pulse is opposite to that of a reset pulse.
Based on the current state of RRAM and other forms of variable resistance memory, there is a general need for improved storage capacity, integration density, and general operating characteristics. Accordingly, RRAM is expected to be a subject of continuing research efforts.